Method and system for utilizing heat in a plant or animal growing device, and greenhouse

ABSTRACT

A method for utilizing heat in a plant or animal growing device includes circulating a heat transfer fluid through a circuit forming a closed fluid loop, heating, via a heat source, the heat transfer fluid in the fluid circuit to a temperature within an efficient operating range of a first heat unit, supplying heat from the heat transfer fluid to a first heat unit, the first heat unit cooling down at least part of the heat transfer fluid to a temperature within an efficient operating range of at least one additional heat unit connected in serial arrangement with the heat source and the first heat unit, supplying heat from the heat transfer fluid from the first heat unit to the additional heat unit, the additional heat unit cooling down at least part of the heat transfer fluid, and returning the cooled down part of the heat transfer fluid from the additional heat unit to the heat source in the fluid circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/239,766, filed Apr. 15, 2014, which is a national stageapplication of PCT/IB2012/001493, filed Aug. 3, 2012, which claimspriority to Australian Patent Application No. AU 2011213783, filed Aug.19, 2011, each of which is expressly incorporated herein in its entiretyby reference thereto.

FIELD OF INVENTION

The present invention relates to a method and system for utilizing heatin a plant or animal growing device, and a greenhouse.

BACKGROUND INFORMATION

Plant or animal growing devices, such as greenhouses, and artificialwater ponds for growing fish and cattle farms, are in use all over theworld. In such devices, energy in the form of heat is used by severalheat users, such as a heating unit, that serves to provide an adequatetemperature of the medium in which the specific type of plant or animalgrows (typically air or water). The heat source may obtain its energy inany manner, typically by burning fossil fuel or by catching solar power.The heat users may vary according to the geographical circumstances,such as the availability of fresh water or seawater. For example, one ofthe heat users may be a thermal desalination unit, in locations whereseawater is abundant and fresh water is scarce.

European Patent No. EP 1 071 317 describes a greenhouse and a heatsource for producing steam comprising at least one collector situatedabove rotatable mirrors which can follow the movement of the sunaccording to the seasons and can make the top-side of the greenhousepractically light-tight. The water, in the form of steam, produced inthe collector is distributed to two heat users, in a ratio determined byvalves, and flows, after condensation, back to the heat source. The twoheat users are (1) a thermal desalination unit and (2) a steam turbine,for producing electricity. The produced desalinated water is used forgrowing plants in the greenhouse. Part of the solar radiation enters theinner space of the greenhouse, where it is used for photosynthesis ofplants.

SUMMARY

The method and device described above do not use the energy of the heatsource in an optimal manner. An objective of the present invention is toprovide a method and device which make more efficient use of the energyof the heat source.

According to an example embodiment of a method and device of the presentinvention, by adding at least one additional heat user in a serialarrangement of the heat users, it becomes possible to arrange the heatusers in such a manner that the heat transfer fluid arriving at them hasa temperature within an efficient operating range of each of the heatusers, without having to dump or otherwise degrade, or diminish, theusability of the heat in the heat transfer fluid. As a result, themethod offers a more efficient use of the heat from the heat source inthat, for example, the heat in the heat transfer fluid can be used moreefficiently, i.e. less heat can be thrown away (to the environment) orreduced in quality or usability by mixing it with colder fluids. Thismay be understood, for example, by comparing the serial arrangement to aparallel arrangement of the heat users: in a serial arrangement, thefull temperature difference, or, in an analogy to an electrical circuit,the full heat “potential”, is used for each heat user, although mostheat users will operate only in their most efficient manner whenoperated at a subrange of said full temperature difference. By arrangingthe heat users serially, and in an appropriate order, they optimally usethe heat in the fluid. This includes optimal use of the energy, i.e.,the amount of energy that can be withdrawn from the heat transfer fluidwith respect to the conditions (such as temperature, pressure,electrical potential) of the environment it operates in. Advantageously,a thermal desalination device may allow such an optimal arrangement witha number of other heat users. Heating by the fluid is to be understoodto include, in particular, flowing the fluid through the component aswell as flowing the fluid through a heat exchanger that is thermallyconnected to the component.

Further, since more efficient use is made of the heat source, a smallerheat source will suffice. As a result, lower investment costs becomepossible for a device that has the same growing capacity.

Furthermore, supply of heat to a heat user may also be indirect, such asvia a heat exchanger or via a secondary medium in a circuit and two heatexchangers.

In an embodiment according to a method and device of the presentinvention, the heat transfer fluid temperature ranges in the heat usersare within the optimal operating temperature ranges of the respectiveheat users in the fluid circuit and, for all heat users in the closedfluid circuit, the heat fluid outlet temperature of one component,whether a heat user or the heat source, equals the heat fluid inlettemperature of the next component. In this manner, the heat produced inthe heat source may be fully used in the heat users, without heat beingdumped outside the heat users.

In another embodiment according to a method and device of the presentinvention, the additional heat user is a heating device of the mediumwhere the plants or animals grow, in particular a crop heating or spaceheating in which the heat transfer fluid in operation is cooled downfurther from a starting temperature equal to or lower than the outlettemperature of the thermal desalination unit. In this manner, thethermal desalination unit and the crop or space heating may makeefficient use of the available heat, due to their aligned operatingtemperatures.

In another embodiment according to a method and device of the presentinvention, the additional heat user is a salt production deviceproducing salt from the brine created in the thermal desalination unitin which the heat transfer fluid in operation is cooled down furtherfrom a starting temperature equal to or lower than the outlettemperature of the thermal desalination unit. This may be another energyefficient arrangement, of two components that in practice are often usedtogether, in order to make both fresh water and brine from seawater andto simultaneously make salt from the brine. The fresh water then may beused in the plant or animal growing device, and the salt may be eitherused or sold.

Alternatively, or in addition, the additional heat user may be a steamcycle machine, in particular an organic rankine cycle machine, in whichthe heat transfer fluid in operation is cooled down from a startingtemperature lower than or equal to the outlet temperature of the heatsource to a temperature lower than or equal to the inlet temperature ofthe thermal desalination unit. A steam cycle machine, especially anorganic rankine cycle machine may be, among other applications, usefulfor producing electricity, or for producing mechanical power that may beused for fresh water production in a reverse osmosis process (e.g., adesalination process driven by mechanical pressure). In combination withthe thermal desalination unit, it not only makes efficient use of theheat from the heat source, but also serves to provide electricity forthe plant or animal growing device. This is in particular the case whenthe heat source is a solar driven heat source, for example driven byconcentrated solar power. With a solar driven heat source usingconcentrated solar power, temperatures of up to 400 degrees Centigrademay be obtained e.g., temperatures at which it is possible to drive anorganic rankine cycle machine running on an appropriately selectedorganic working medium. Furthermore, a thermal desalination unit, in anexample embodiment, operates relatively efficiently at heat transferfluid inlet temperatures of about 90-120 degrees Centigrade,temperatures typically available at the outlet of an organic rankinecycle fed at around 50-300 degrees Centigrade.

In another embodiment according to a method and device of the presentinvention, at least part of the heat in the circuit is temporarilystored in a heat buffer and then used in at least one of the heat users.This may be particularly useful when one or more heat users temporarilydo not need any heat; the heat from the heat source, or from anotherheat user upstream from the specific heat user(s) temporarily not used,or used at a reduced power, may then be stored until it is needed.

Moreover, by using a buffer, temporary peak demands from a heat user maybe accommodated for. This provides a method that is more efficient thanwhen a heat user is simply by-passed.

In a further embodiment according to a method and device of the presentinvention, the heat source is a solar driven heat source, in particularutilizing concentrated solar power. Such heat sources combine well withthermal desalination units in the circuit, with respect to thermodynamicefficiency.

In a further embodiment according to a method and device of the presentinvention, a vertical buffer tank is present, and a natural temperaturegradient arises in the vertical direction, due to temperature-relateddensity differences in the fluid.

In addition, a direct fluid communication may occur in which fluidcommunication between two components, being heat sources or heat users,without passing other heat sources or heat users (valves and tubes arenot regarded as heat sources or heat users).

In a further embodiment according to a method and device of the presentinvention, in a greenhouse, a serial arrangement of a thermaldesalination device with other heat users, in particular the heating ofthe air in the greenhouse and possibly an organic rankine cycle and/or asalt production device, make a high energy efficiency possible.Moreover, it becomes possible to obtain a lower cost price of thesystem.

Exemplary embodiments of the present invention will now be describedwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a first embodiment of the system according tothe invention.

FIG. 2 schematically shows a second embodiment of the system accordingto the invention.

DETAILED DESCRIPTION

An exemplary embodiment of a system S1, S2 which is part of a greenhousefor growing plants of the present invention is described with referenceto FIGS. 1 and 2.

The system S1 includes tubes, or piping, 1 represented by lines. Thesystem S1 also contains a solar collector 2 that makes use of opticalmirrors (not shown) to concentrate incident solar rays on a fluid line,and as such, to heat the fluid in the fluid line of the solar collector.The solar collector 2 is part of a fluid loop which includes the tubes1, valves 3, a thermal desalination unit 4, a salt production unit 5, aheat exchanger 6 for a greenhouse air space heating 7 and an electricalpump 8. Arranged parallel to the line with the solar collector 2 and thepump 8 is a line with a heat buffer tank 9 and a pump 10. Line 11 is abypass line for the thermal desalination unit 4. Line 12, between thebuffer tank 9 and the salt production unit 5, connect the buffer tank 9with the salt production unit 5 and the heat exchanger 6. The heatexchanger 6 is part of a second fluid loop 13, which loop 13 serves as athermal connection between the heat exchanger 6 and the space heating 7of the greenhouse.

The salt production unit 5 may be a multi stage flash unit, with anoperating temperature between 70 and 110 degrees Centigrade.Alternatively, it may be a high performance salt production device withplastic heat exchangers that may have a slightly lower operatingtemperature, or it may be an open salt pond which may have an even loweroperating temperature, where water evaporates from brine, and saltremains.

The buffer tank 9 is a vertical tank, of which a fluid inlet 14 islocated at its top end and connected to the heat source outlet 15. Afluid outlet 16 of the buffer tank 9 is located at its bottom end andconnected to the heat source inlet 17. The vertical buffer tank 9 hasone fluid outlet 18 at its top end, connected via pump 10 to the thermaldesalination unit 4, and has four fluid outlets 19 connected to inlets20 and 21 of the salt production unit 5 and the heat exchanger 6,respectively. Each of the fluid outlets 19 is located at a differentheight between the top and bottom ends of the buffer tank 9, allowingfor different take-off temperatures at the different fluid outlets 19when a vertical temperature gradient is present within the buffer tank9.

In the method according to an example embodiment of the presentinvention of system S1, a heat transfer fluid, such as glycol, iscirculated through the heat users, in a serial arrangement, i.e., oneafter the other, i.e. through the thermal desalination unit 4, the saltproduction unit 5, and the heat exchanger 6 of the greenhouse air spaceheating 7.

The fluid is heated in the solar collector 2, to a temperature of up to400 degrees Centigrade, then, in normal operation mode, passes throughthe heat exchanger of the thermal desalination unit 4, giving heat tothat unit.

The fluid leaves the heat exchanger at around 70-110 degrees Centigrade,and enters the salt production unit 5, cools down further and continuesto the heat exchanger 6 at a temperature between 50-90 degreesCentigrade. It returns to the solar collector 2 at a temperature between20-70 degrees Centigrade, where it starts a new cycle through the fluidcircuit.

It is possible to change the described normal operation mode to otheroperation modes, by, e.g., closing and opening valves 3 and activatingor stopping pumps 8 and 10.

Via tubes 1 and pump 10 heat transfer fluid may be tapped from thebuffer tank 9 and may be fed to the thermal desalination unit 4. Thismay be useful when the solar collector 2 may not be providing enoughheat and/or provides heat at inadequate temperatures for the thermaldesalination unit 4 to operate or to operate optimally, for instance,during nighttime conditions.

Via tubes 12 the buffer tank 9 may be tapped at different heights, andthe tapped fluid may be mixed with the fluid from the solar collector 2entering either the salt production unit 5 or the heat exchanger 6. Thismay temporarily lead to some loss of energy, but may make it possible tooperate these two heat users within their allowed temperature ranges,and thus, to operate the whole system Si, without having the need for abackup system. Moreover, adding fluid from the buffer tank 9, may allowfor driving the heat users at their optimal temperature ranges, withrespect to life expectancy and/or energy efficiency, thereby savingeither investment costs or energy costs, or both.

A bypass tube 11 allows for bypassing of the thermal desalination unit4, for instance when the thermal desalination unit 4 may be subject tomaintenance operations.

FIG. 2, shows the system S2, which is similar to the system S1 of FIG. 1but has an additional heat user, in the form of a turbine 25 of anorganic rankine cycle. The heat exchanger of the thermal desalinationunit 4 serves as the condenser of the organic rankine cycle; thus, thecycle is integrated in the fluid circuit of system S2. The turbine 25 ismechanically coupled to a generator 26 of electricity.

Salt production unit 5′ is a high-performance salt production devicewith plastic heat exchangers, operating at lower temperatures than themultistage flash unit 5 of FIG. 1.

Pump 10 of system S1 is replaced by pump 27 integrated in tubes 12′connecting the buffer tank 9 to an inlet 20, 21, 28, 29 of each of theheat users.

In the method according to an example embodiment of the presentinvention of system S2, a heat transfer fluid, e.g., an organic fluidwith a high molecular mass and a boiling point below that of water inthe atmosphere, is circulated through the heat users, i.e. through theorganic rankine cycle turbine 25, thermal desalination unit 4, the saltproduction unit 5, and the heat exchanger 6 of the greenhouse air spaceheating 7. The fluid is heated and evaporated in the solar collector 2,to a temperature up to 400 degrees Centigrade, then, in normal operationmode, passes through the turbine 25 of the organic rankine cycle, whereit may lose energy, in terms of both pressure and heat, while drivingthe generator 26 and thereby producing electricity for the greenhouseclimate control equipment (fans, pumps, etc.) and other electricalequipment. Next, the fluid enters at a temperature between 90-130degrees Centigrade, a heat exchanger of the thermal desalination unit 4and condenses while giving heat to the desalination unit 4. The fluidleaves the heat exchanger between 70-110 degrees Centigrade, and entersthe salt production unit 5′, cools down further and continues to theheat exchanger 6 at a temperature between 50-90 degrees Centigrade. Itreturns to the solar collector 2 at a temperature between approximately20-70 degrees Centigrade, where it starts a new cycle through the fluidcircuit.

It is possible to change the described normal operation mode to otheroperation modes, by, e.g., closing and opening valves 3 and activatingor stopping pumps 8 and 27.

Via tubes 12′ the buffer tank 9 may be tapped at different heights, andthe tapped fluid may be mixed with the fluid from the solar collector 2entering any of the heat users. The reasons for doing so are describedabove with respect to system S1.

Not shown in FIG. 2, are bypass tubes in each of the heat users. Thesebypass tubes may allow the system S2 to operate when one of the heatusers may temporarily not be used, e.g. because there may be no heatdemand or during maintenance activities. Alternatively, the tubes 12′may be used as bypass tubes.

Also not shown in FIGS. 1 and 2, is an additional heat source, operatingon fossil fuel and arranged in parallel and or series to the solarcollector 2. This additional heat source provides heat at moments whenthe demand is higher than the solar collector 2 is capable of supplying.

The described and shown embodiments of the invention serve forillustration of the invention. Variations on these embodiments arepossible. For example, a buffer container may be interposed between twoheat users, instead of between the outlet and inlet of the heat source.Also, a heat user may be composed of a heat exchanger with an attachedsecond fluid circuit as a closed loop that comprises two or more heatusers, for example, in order to be able to apply different fluidpressures in each of the fluid loops. This is in particular useful forkeeping the organic rankine cycle in FIG. 2 as a separate loop, fed by aheat exchanger through which the heat transfer fluid from the solarcollector 2 flows.

What is claimed is:
 1. A method for utilizing heat in a plant or animalgrowing device, comprising: circulating a heat transfer fluid through acircuit forming a closed fluid loop; heating, via a heat source, theheat transfer fluid in the fluid circuit to a temperature within anefficient operating range of a first heat unit; supplying heat from theheat transfer fluid to a first heat unit, the first heat unit coolingdown at least part of the heat transfer fluid to a temperature within anefficient operating range of at least one additional heat unit connectedin serial arrangement with the heat source and the first heat unit;supplying heat from the heat transfer fluid from the first heat unit tothe additional heat unit, the additional heat unit cooling down at leastpart of the heat transfer fluid; and returning the cooled down part ofthe heat transfer fluid from the additional heat unit to the heat sourcein the fluid circuit.
 2. The method according to claim 1, wherein: aheat fluid outlet temperature of one of the respective heat unit and theheat source equals a heat fluid inlet temperature of a following one ofthe respective heat unit and the heat source.
 3. The method according toclaim 1, wherein the first heat unit includes a thermal desalinationunit, the additional heat unit includes a heating device of a medium ofthe plant or animal growing device, and wherein the heat transfer fluidis cooled down further to a temperature equal to or lower than an outlettemperature of the thermal desalination unit.
 4. The method according toclaim 3, wherein the heating device includes a crop heating deviceand/or a space heating device.
 5. The method according to claim 1,wherein the first heat unit includes a thermal desalination unit, theadditional heat unit includes a salt production device for producingsalt from brine created in the thermal desalination unit, and whereinthe heat transfer fluid is cooled down further to a temperature equal toor lower than an outlet temperature of the thermal desalination unit. 6.The method according to claim 1, wherein the first heat unit includes asteam cycle machine, the additional heat unit includes a thermaldesalination unit, and wherein the heat transfer fluid is cooled by thefirst heat unit down from a starting temperature lower than or equal toan outlet temperature of the heat source to a temperature lower than orequal to an inlet temperature of the thermal desalination unit.
 7. Themethod according to claim 6, wherein the steam cycle machine includes anorganic rankine cycle machine.
 8. The method according to claim 1,wherein at least part of the heat transfer fluid is temporarily storedin a heat buffer for later use in at least one of the heat units.
 9. Themethod according to claim 1, wherein the heat source includes a solardriven heat source which is driven by concentrated solar power.
 10. Asystem for utilizing heat in a plant or animal growing device,comprising: a fluid circuit including a pump and forming a closed fluidloop, wherein the pump is configured to circulate heat transfer fluidthrough the fluid circuit; a heat source configured to add heat to theheat transfer fluid in the fluid circuit; and a first heat unitconfigured to be heated by the heat transfer fluid in the fluid circuitto an efficient operating range of temperature of the first heat unit;at least one additional heat unit connected in serial arrangement withthe heat source and the first heat unit, configured to be heated by theheat transfer fluid in the fluid circuit from the first heat unit to anefficient operating range of temperature of the additional heat unit.11. The system according to claim 10, wherein the first heat unitincludes a thermal desalination unit, the additional heat unit includesa heating device of a medium of the plant or animal growing device, andwherein the additional heat unit is disposed between an outlet of thethermal desalination unit and an inlet of the heat source.
 12. Thesystem according to claim 11, wherein the heating device includes a cropheating device and/or a space heating device of a greenhouse.
 13. Thesystem according to claim 10, wherein the first heat unit includes athermal desalination unit, the additional heat user includes a saltproduction device for producing salt from brine created in the thermaldesalination unit.
 14. The system according to claim 13, wherein thesalt production device includes a salt pond.
 15. The system according toclaim 10, wherein the first heat user includes a steam cycle machine,the additional heat unit includes a thermal desalination unit, andwherein the first heat unit is disposed between an outlet of the heatsource and an inlet of the thermal desalination unit.
 16. The systemaccording to claim 15, wherein the steam cycle machine includes anorganic rankine cycle machine.
 17. The system according to claim 10,further comprising a heat buffer having a fluid inlet and at least onefluid outlet, wherein the fluid inlet is in direct fluid communicationwith the fluid circuit, and the at least one fluid outlet is in directfluid communication with a fluid inlet of the heat unit and/or of the atleast one additional heat unit.
 18. The system according to claim 17,wherein the heat buffer includes a vertical tank, and wherein thevertical tank includes: the fluid inlet; and at least one heat transferfluid take-off outlet disposed at a height between a top end of thevertical tank and a bottom end of the vertical tank, wherein the atleast one heat transfer fluid take-off outlet is in direct fluidcommunication with the fluid circuit, wherein the height between the topend of the vertical tank and the bottom end of the vertical tank isselected such that a temperature of the heat transfer fluid at arespective one of the at least one heat transfer fluid take-off outletis equal to or approximate to a temperature of the heat transfer fluidin a respective heat unit at a location where the heat transfer fluidfrom the respective take-off outlet is added to the fluid through therespective heat unit.
 19. The system according to claim 10, wherein theheat source includes a solar driven heat source.
 20. A greenhouse,comprising the system according to claim
 10. 21. The method according toclaim 1, wherein the first heat unit includes a thermal desalinationunit, the additional heat unit includes a heating device of a medium ofthe plant or animal growing device, a salt production device forproducing salt from brine created in the thermal desalination unit,and/or a steam cycle machine.
 22. The method according to claim 21,wherein at least part of the heat transfer fluid is temporarily storablein a heat buffer for later use in at least one of the heat units,wherein the heat buffer includes a vertical tank, and wherein thevertical tank includes: a fluid inlet disposed at a top end of thevertical tank and connected to an outlet of the heat source; at leastone heat transfer fluid take-off outlet disposed at a bottom end of thevertical tank and connected to an inlet of the heat source; and at leastone fluid outlet connected to an inlet of a respective heat unit. 23.The method according to claim 1, wherein at least part of the heattransfer fluid is temporarily storable in a heat buffer for later use inat least one of the heat units, wherein the heat buffer includes avertical tank, and wherein the vertical tank includes: a fluid inletdisposed at a top end of the vertical tank and connected to an outlet ofthe heat source; at least one heat transfer fluid take-off outletdisposed at a bottom end of the vertical tank and connected to an inletof the heat source; and at least one fluid outlet connected to an inletof a respective heat unit.
 24. The system according to claim 10, whereinthe first heat unit includes a thermal desalination unit, the additionalheat unit includes a heating device of a medium of the plant or animalgrowing device, a salt production device for producing salt from brinecreated in the thermal desalination unit, and/or a steam cycle machine.25. The system according to claim 24, wherein at least part of the heattransfer fluid is temporarily storable in a heat buffer for later use inat least one of the heat units, wherein the heat buffer includes avertical tank, and wherein the vertical tank includes: a fluid inletdisposed at a top end of the vertical tank and connected to an outlet ofthe heat source; at least one heat transfer fluid take-off outletdisposed at a bottom end of the vertical tank and connected to an inletof the heat source; and at least one fluid outlet connected to an inletof a respective heat unit.